Defect # 1. Distortion:

Distortion, war page, and buckling of the welded parts are welding defects result of residual stresses.

They are caused by the result of:

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(i) Restraining the free movement of some parts or members of the welded structure.

(ii) Non-uniform expansion and shrinkage of the metal in the weld area as a consequence of uneven heating and cooling.

(iii) The base metal may be pulled out of original alignment.

This defect may be controlled or eliminated by:

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(i) Closing the distance between two plates.

(ii) Better alignment of the plates to be welded.

(iii) Increasing the welding speed.

(iv) Proper clamping of the plates, etc.

Defect # 2. Porosity:

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Porosity can take form of blow-holes, gas pockets, tiny spherical holes, in the weld puddle.

These defects are caused by:

(i) Evolution of gases during welding or releasing of gases during solidification.

(ii) Excess sulphur or sulphide in steels, because they generate gases during welding that are often entrapped in the molten metal.

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(iii) Presence of hydrogen, contamination of the joint, contaminants in the flux, etc.

This defect may be controlled or eliminated by:

(i) Maintaining clean work piece surfaces.

(ii) Properly conditioning the electrodes.

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(iii) Reducing welding speed.

(iv) Eliminating any moisture on work pieces.

(v) Avoiding the use of a base metal containing sulphur or electrodes with traces of hydrogen, etc.

Defect # 3. Cracks:

Welding cracks belongs to two main groups: Fusion zone cracks and heat-affected zone cracks. The first group known as Hot-cracking includes longitudinal and transverse cracks as well as cracks appearing at the root of the weld bead. This type of cracking occurs at elevated temperatures just after the molten metal starts to solidify.

It is especially found in ferrous alloys with high sulphur and phosphorous contents and in alloys having large solidification ranges.

The second group of cracking, heat affected zone cracks, is also known as Cold-Cracking. This defect is caused by excessive brittleness of the heat affective zone that is due to hydrogen embrittlement or due to martensite formation as a result of rapid cooling. This defect is especially found in high-carbon and alloy-steel welded joints.

These cracks may be controlled or eliminated by:

(i) Controlling the cooling rate of the welded joint to keep it a minimum e.g., keep joints in a furnace after welding or embed them in sand.

(ii) Pre-heating the parts and maintaining the pre-heating temperature till the weld is complete.

(iii) Correct joint design.

(iv) Reliving the stresses by pre-welding and post-welding heat temperature.

(v) The use of multiple pass in welding, as each pass would provide a sort of pre-heating for the followed pass.

Defect # 4. Slag Inclusion:

Slag inclusion includes the entrapment of the slag in the solidify weld metal. This defect may occur in single-pass as well as in multi pass welds and resulting into a joint of poor strength.

This defects may caused by:

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(i) Improper manipulation of electrode due to turbulence of molten metal the slag pushed ahead of the arc into the molten-metal pool, where it becomes entrapped in the solidifying weld metal.

(ii) In multi-pass welds, slag inclusions are caused by improper removal of the slag blanket after each pass.

(iii) Contaminants in the base metal.

(iv) Non-uniform melting of electrode coating.

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(v) High-viscosity of slag and/or molten metal.

(vi) Too-rapid solidification of molten metal which does not provided the time to float the slag.